Typical hot-fed extruders are made up of a feed hopper cylinder and one or more forward (downstream) cylinders or sections assembled together in axial alignment. In addition, there is often a separate drive adapter located upstream of the hopper cylinder. This drive adapter enables a reduction gear transmission unit to be coupled to the extruder barrel and to the extruder feed screw for rotating the feed screw about its axis within the barrel.
During assembly of an extruder made up of these multiple parts or sections, it is necessary to obtain a close axial alignment from piece-to-piece and also to achieve a close alignment of the whole extruder barrel assembly made up of these multiple parts so as to provide a straight bore for the extruder barrel. The reason why a close axial alignment of the extruder barrel components is necessary is that an extruder feed screw is inserted into the barrel bore along its axis. During operation of the extruder, this feed screw is rotated with its helical flights revolving closely spaced from the inner surface of the bore within the extruder barrel. A close alignment is necessary to prevent interference or gouging between the rotating feed screw and the inside surface of the extruder barrel.
Such an alignment procedure is very time consuming and costly. Many times it becomes necessary to remove one of the assembled extruder barrel sections and to have it re-machined in order to obtain the correct axial alignment for the whole assembled extruder barrel.
Moreover, there have been reports of leakage of molten plastic during operation of hot-fed extruders. The molten plastic is reported to leak out of the barrel through the joints or split lines between adjacent sections prior art of hot fed extruder barrels.